GB 142 and indirect question??

Dave_22

I put in a GB-142 and ST 40 gallon indirect. I put in a 3 speed Grundfos circulator instead of a taco 0011. When filling the big tub it sometimes runs out of hot water. I thought it could be the pump but the delta T on the boiler in and out of the hot water tank is almost the same. It's like it is not giving off any of it's heat to the tank- i found that a little odd. You could take four showers in a row and have plenty of hot, the problem is only with the big tub and only when the water hasn't been reheated in a while. I'm sure I can fix by heating the tank to 140 and mixing down, I just don't understand why such a small delta T when trying to reheat cold water- any thoughts?

EBEBRATT-Ed

Is it possible that your pumping to fast??

Ed

Mike C_3

??

i was thinking the same thing. what speed to you have it on and which GB do you have?24-60??
If the pump speed is too high you push the btu right out before it can heat the indirect.

Kevin__Flynn

How big...

is the tub? What is the flow rate of the tub filler? What temp is the water stored at?

It is not uncommon to see a tub filler in excess of 10 GPM's. If it is indeed a 10 GPM filler you could potentially draw down the tank in a matter of 3-4 minutes. If your tub is greater than let's say, 50 gallons this could be a problem.


Kevin Flynn

Dave_22

Hmmm...

I do have it on the highest speed- I could try slowing it down and see how it responds. Another wierd thing is the boiler water temp only raises to about 170. If the BTU's aren't getting into the water, and the boiler is firing at high fire, wouldn't that temperature skyrocket?

Mike T., Swampeast MO

Have you checked the boiler settings for DHW production? The boiler temp may well be adjustable and it might not be set as high as possible.

You said the problem only occurs after the indirect has sat for a good period without firing from the boiler. That makes me think that the water is naturally cooling and stratifying. Then you're drawing water faster than it can be heated. Can you adjust the differential temperature for heating the indirect? If so, try a tighter differential by raising the cut-in temp. If you can't adjust the differential or doing so doesn't help, can you raise the cut-out temp?

Dave_22

I don't know if i can adjust the differential- i don't see anything in the manual- i guess i need Joe from Buderus to help on this one. I can raise the cut cut out temp by adjusting the dial on the BC controller, but i will have to mix the water down so it doesn't burn anyone. As far as i know, on a DHW call the GB goes to maximum fire and there is no adjusting it-unless someone knows different???

Joe@buderus_2

GB142

The DHW differential is fixed at seven degrees. It cannot be changed. On a call for DHW the GB142 will go to max temperature of 194 degrees. What size GB142 and 3 speed circulator is being used?

Dave_22

GB-142/24 and i believe a 15-58IFC

J.C.A._3

Big draw....

In a short time, and the boiler makes water hot better than than the coil can dispurse it.
Maybe the DHW tank should have been bigger to start with? I'd say that bumping the temp. and mixing down the outlet is your only saving grace at this point. (measure the flow from the faucet in a 5 gallon bucket and clock it as far as GPM, and I bet you'll get your answer real quick) Some of these faucets can dump copius amounts of water and if the tank gets depleted, what other choices do you have?

To quote GrandPah, you'll also be eliminating the risk of Leigionella....win/win, and the cost is minor. Chris

Mike T., Swampeast MO

Sure sounds like you're running out of hot water.

Given Joe's operational comments and your observation that boiler temp is only 170° or so during such a call it would seem that you're sucking up the BTUs just as fast as they can be produced with a rapid influx of cold water keeping the HX temp down.

Have you verified that the boiler is operating at full input? If natural gas, the 1/2 foot dial should rotate about 5 1/3 times in two minutes if the boiler is operating at max input of about 85,000 btu/hr.

Is the boiler temp during a non-tub related DHW call higher?

Ray Landry_2

You need to use a grundfoss 2664 circulator or equivilent to move proper gpms between the boiler and hot water tank. (on a call for dhw your primary pump shuts off this is why the dhw pump needs to over come the gpm/head loss requirments of the tank and boiler) This could be the reason your gb wont go above 170* on a call for dhw. It may not be seeing a rapid enough movement of the water... it's interesting though that your delta t is so minor... are you taking this from the surface temps of the inderect loop? If so what is an average delta t on a minor call for dwh

Mike T., Swampeast MO

I was thinking about that too Ray.

Please correct me if I'm wrong, but if flow were insufficient AND the boiler is operating at max output wouldn't the temp go to max as well? Wouldn't this make the boiler either cycle or reduce output? If reduced ouput wouldn't it be at/near max temperature?

Joe@buderus_2

GB142

The head pressure through the GB142/24 at 8gpm is approximately 6 1/2 feet of head. The pressure drop through the tank coil is approximately 3 feet of head. Include piping loss (minimal) to size the circulator. We would recommend a Grundfos UP26-64 with the GB142/24 and the ST150.It is also suggested to determine the faucets gpm.

Dave_22

I understand what is recommended, but wouldn't you think that if there was not enough flow, that the delta T across the indirect would be very large? It seems like the tank is not "sucking" the heat out of the boiler loop.

Mike T., Swampeast MO

That's what I'd think as well but these boilers are awfully smart and might make decisions (like reducing output) if things don't "seem right" during DHW operation.

If natural gas, I'd clock the meter to verify input at/near maximum.

If LP, isn't there a test "chimney sweep" mode? Doesn't it fire at full input? Compare sound levels. I know it's a very quiet boiler, but surely sound increases somewhat as the draft inducing fan increases speed.

Dave_22

It is LP- i will have to check out the "chimney sweep" test. Boiler aside, i would think if the boiler water going into the indirect is close to the same as the boiler water coming out- sutin ain't right!!!!

Mike T., Swampeast MO

I'd check the manual to make sure that the "chimney sweep" mode is full fire--if memory serves it is, but I can't be certain. I've read the manuals, but didn't print and haven't used the boiler.

GW

Joe,

Hey Joe, long time no chat,

If one used the boiler header that comes with the boiler, why does he need to consider the pres drop on the boiler?

gary

Dave_22

Even with this header a seperate pump that pumps directly through the boiler is required.

Dave_22

flow

Well- i did a bucket test and was flowing about 3-3.5 GPM a minute of hot water. I guesstimated that the tub holds about 30 gallons of water. Now i'm a little more baffled.

Mike C_3

Gary

Because when there is a domestic call the header and radiant pumps stop and the domestic pump takes over.